A study on the position control problem of the nonlinear hydraulic servo system subjected to unknown and time-varying external load disturbances was executed. Since there exist nonlinearties of the hydraulic system itself and the uncertainties of the external load disturbances resulting from the interaction between the process dynamics and the hydraulic actuator motion, the conventional controller design approach may not assure satisfactory control performances. To obtain better performances an adaptive modelling following control scheme was derived, based upon the Liapunov's Direct Methods[8]. In order to deal with the uncertainties that are associated with the plant dynamics and the unknown disturbances, this method utilizes an ultimate boundness of the uncertain parameters as an adaptation criterion. The response characteristics of the derived adaptive controller with various external disturbances are investigated and compared with that of the conventional controller theoretically and experimentally.
In order to investigate the possibility of the application of the derived adaptive controller to the real process a disturbance simulation system which can simulate the external load disturbance acting on the hydraulic servo system was proposed. This system employs an electro-magnetic relief valve which controls a pressure in a sub-cylinder and generates the force equivalent to a desired external load disturbance. With the help of such device, the experimental investigation of the performance characteristics of the derived adaptive controller becomes possible.
The theoretical and experimental results show that this proposed AMFC is fairly robust to the unknown and time-varying external load disturbances and yield much better performance characteristics as compared with the conventional PI controller with constant feedback gain.
